The present invention relates to a granular material color sorting apparatus which optically detects and removes bad grains in cereal grains such as rice grains, wheat grains or the like. The "bad grain" used herein means colored grains such as degenerated cereal grains, and foreign matters such as pieces of glass or stones in similar color to good cereal grains or transparent.
The granular material color sorting apparatus to be improved by the invention comprises a feed device for material grains, a transfer device adapted to make the material fed from the feed device flow down, an optical detector unit mounted near the terminal end of the transfer device, an injection nozzle device mounted along the path of falling-down of the material from the transfer device, and a control unit connected to the optical detector unit and the injection nozzle device. In this sorting apparatus, the material grains fall down from an inclined sliding surface of the transfer device through a substantially constant locus, and the optical detector unit optically detects the material grains. The control unit discriminates good and bad grains based on the optical detection value, and activates the injection nozzle device to blow off the bad grains. Thus, the bad grains are sorted from the material grains.
When it is intended to sort colored grains and foreign matters in the material, the optical detector unit uses a visible light sensor for detecting the colored grains, and a near infrared sensor for detecting glass or stones. Such granular material color sorting apparatus is found, for example, in U.S. Pat. No. 5,638,961 of the same assignee as the present invention.
In this case, the control unit has a comparator, an injection time control section, and an injection delay control section. The comparator compares a detected value of the optical detector unit with a predetermined threshold to discriminate bad grains from good grains. The injection time control section activates the injection nozzle device for a predetermined period of time to inject air. The injection delay control section delays the operation of the injection nozzle device for a predetermined period of time after detection of a bad grain. In operation, as shown in FIG. 9, if detection signals S1 and S3 from the near infrared sensor 130 and a detection signal S2 from the visible light sensor 120 exceed thresholds, the comparator 140 determines them as bad grains, and outputs signals N1, N2 and N3 indicating the bad grains. The injection delay control section 180 and the injection time control section 190 output signals T1, T2 and T3 of a fixed delay time t, as well as signals F1, F2 and F3 of a fixed injection time f in response to the bad grain signals N1, N2 and N3, respectively, to activate the injection nozzle device.
By the way, a foreign matter such as glass or a stone, as compared with a good cereal grain or a colored cereal grain, is higher in specific gravity and lower in frictional resistance when flowing down on the sliding surface of the transfer device, so that it falls down from the transfer device at a higher speed. Therefore, when the comparator determines a bad grain, the injection delay control section 180 activates the injection nozzle device at a relatively short period of delay time or timing for enabling capture of glass or a stone of a higher falling-down speed. On the other hand, the injection time control section 190 outputs an injection time f for enabling capture of even a colored cereal grain of a lower falling-down speed so as to remove the bad grain. As described, one activation of the injection nozzle device is necessary to have a long injection time f so that bad grains being determined can be removed regardless of colored cereal grains or foreign matters such as glass or stones, and thus consumes much air. In addition, there is a problem that, since the injection time f is long, good cereal grains before and after a bad grain are also removed by an injected air flow in a higher ratio, and it becomes impossible to sort only bad grains.
In this connection, Japanese Utility Model Application Laid-Open Publication No. 6-41876 proposes a sorting apparatus varying a driving time and a driving delay time for air injection depending on the lengths of objects to be sorted. This apparatus is for small objects such as pharmaceuticals or electronic components, has an optical detector unit for sensing the length of an object to be sorted, and is provided in an air nozzle driving system with means for changing the activation time of an air nozzle in response to its detection signal.
The sorting apparatus described in this publication is so constructed as to control the injection or drive time and/or the delay time of the air nozzle driving system depending on a detection signal of length of an object to be sorted. Therefore, the apparatus may effectively sort bad ones different from good articles only in size, but may not sufficiently sort colored grains or foreign matters such as glass or stones of different falling-down speeds.